proxy crash with no abort controller

Author: evalstate

src/examples/client/disconnectTestClient.ts

@@ -0,0 +1,34 @@
+import { Client } from '../../client/index.js';
+import { StreamableHTTPClientTransport } from '../../client/streamableHttp.js';
+import { CallToolResultSchema } from '../../types.js';
+
+const client = new Client({ name: 'disconnect-test-client', version: '1.0.0' });
+const transport = new StreamableHTTPClientTransport(new URL('http://localhost:3000/mcp'));
+
+let progressCount = 0;
+
+client.onerror = e => console.error('Client error:', e);
+
+(async () => {
+    await client.connect(transport);
+    console.log('Connected, calling slow-task with steps=10...');
+
+    try {
+        const result = await client.request(
+            { method: 'tools/call', params: { name: 'slow-task', arguments: { steps: 10 } } },
+            CallToolResultSchema,
+            {
+                onprogress: progress => {
+                    console.log(`Progress ${++progressCount}: ${progress.progress}/${progress.total}`);
+                    if (progressCount === 5) {
+                        console.log('Abruptly killing process after 5 progress updates...');
+                        process.exit(1);
+                    }
+                }
+            }
+        );
+        console.log('Result:', result);
+    } catch (e) {
+        console.log('Request aborted (expected):', (e as Error).message);
+    }
+})();

src/examples/server/disconnectTestServer.ts

@@ -0,0 +1,78 @@
+import { Request, Response } from 'express';
+import { McpServer } from '../../server/mcp.js';
+import { StreamableHTTPServerTransport } from '../../server/streamableHttp.js';
+import { createMcpExpressApp } from '../../server/express.js';
+import { CallToolResult, isInitializeRequest } from '../../types.js';
+import { randomUUID } from 'node:crypto';
+import * as z from 'zod/v4';
+
+const server = new McpServer(
+    { name: 'disconnect-test', version: '1.0.0' },
+    { capabilities: { logging: {} } }
+);
+
+server.tool('slow-task', 'Task with progress notifications', { steps: z.number() },
+    async ({ steps }, extra): Promise<CallToolResult> => {
+        for (let i = 1; i <= steps; i++) {
+            console.log(`Sending notification ${i}/${steps}`);
+
+            // SIMULATING A PROXY RELAY: onprogress forwards with same progress token
+            const progressToken = extra._meta?.progressToken;
+            if (progressToken !== undefined) {
+                server.server.notification(
+                    {
+                        method: 'notifications/progress',
+                        params: { progressToken, progress: i, total: steps }
+                    },
+                    { relatedRequestId: extra.requestId }
+                );
+            }
+
+            await new Promise(r => setTimeout(r, 1000));
+        }
+        return { content: [{ type: 'text', text: 'SUCCESS' }] };
+    }
+);
+
+const app = createMcpExpressApp();
+const transports: Record<string, StreamableHTTPServerTransport> = {};
+
+app.post('/mcp', async (req: Request, res: Response) => {
+    const sessionId = req.headers['mcp-session-id'] as string | undefined;
+    let transport = sessionId ? transports[sessionId] : undefined;
+
+    if (!transport && isInitializeRequest(req.body)) {
+        transport = new StreamableHTTPServerTransport({
+            sessionIdGenerator: () => randomUUID(),
+            onsessioninitialized: id => {
+                console.log(`Session initialized: ${id}`);
+                transports[id] = transport!;
+            }
+        });
+        transport.onclose = () => {
+            console.log(`Transport closed for session: ${transport!.sessionId}`);
+            delete transports[transport!.sessionId!];
+        };
+        await server.connect(transport);
+    }
+
+    if (transport) {
+        // Track if response finished normally
+        let finished = false;
+        res.on('finish', () => { finished = true; });
+        res.on('close', () => {
+            if (!finished) {
+                console.log('Client disconnected - closing transport to reclaim resources');
+                transport!.close();
+            }
+        });
+        await transport.handleRequest(req, res, req.body);
+    } else {
+        res.status(400).json({ jsonrpc: '2.0', error: { code: -32000, message: 'Bad request' }, id: null });
+    }
+});
+
+// Return 405 for GET - we don't support standalone SSE stream
+app.get('/mcp', (_req, res) => res.status(405).send('Method not allowed'));
+
+app.listen(3000, () => console.log('Disconnect test server listening on :3000'));